content: /*
   * Copyright 2016-present David Karnok
   *
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *
   *     http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  
  package hu.akarnokd.rxjava3.util;
  
  import java.util.Objects;
  import java.util.concurrent.atomic.AtomicReference;
  
  import io.reactivex.rxjava3.operators.SimplePlainQueue;
  
  /**
   * A single-producer single-consumer queue with exactly one slot of value.
   *
   * @param <T> the value type
   */
  public final class SpscOneQueue<T> extends AtomicReference<T>
  implements  SimplePlainQueue<T> {
  
      private static final long serialVersionUID = -8766520133280966316L;
  
      @Override
      public boolean offer(T value) {
          Objects.requireNonNull(value, "value is null");
          if (get() == null) {
              lazySet(value);
              return true;
          }
          return false;
      }
  
      @Override
      public boolean offer(T v1, T v2) {
          throw new UnsupportedOperationException();
      }
  
      @Override
      public boolean isEmpty() {
          return get() == null;
      }
  
      @Override
      public void clear() {
          lazySet(null);
      }
  
      @Override
      public T poll() {
          T v = get();
          if (v != null) {
              lazySet(null);
          }
          return v;
      }
  }
  